1. Field of the Invention
This invention relates to a process and apparatus for production of synthetic hydrocarbon fuels from peat wherein the relative liquid-gas outputs may be varied to provide greater proportions of liquid or gaseous fuels as desired, while maintaining highly efficient overall carbon conversion to useful fuel.
Peat is considered to be geologically young coal and has been found extensively throughout the world. European countries and Asian countries have for years extensively used peat as a source of fuel and chemicals. The United States is considered to have the second largest peat resource in the world, but has not used peat commercially as a source of energy. The total energy contained in the United States peat resources is estimated to be equivalent to about 240 billion barrels of oil. Thus, peat is the second most abundant fossil fuel, after coal, in the United States. Peat is of even more significance in the United States since in the contiguous 48 states, the peat deposits are generally located in areas with no significant resources of other fossil fuels. The peat deposits in the United States occur generally at the ground surface, with little or no overburden. Therefore, peat harvesting and land reclamation efforts have been very successful. Large scale utilization of peat, therefore, should have a positive effect upon the environment, the socioeconomic system, as well as providing energy resources.
2. Description of the Prior Art
The potential for production of synthetic natural gas (SNG) from peat has been previously recognized. "Peat Gasification for SNG Production", D. V. Punwani and A. M. Rader, presented at Nine Synthetic Pipeline Gas Symposium, Oct. 31-Nov. 2, 1977, Chicago, Illinois; "SNG Production from Peat", D. V. Punwani, W. W. Bodle, A. M. Rader and P. B. Tarman, presented at Miami International Conference on Alternative Energy Sources, Dec. 5-7, 1977, Miami, Florida; "Peat Gasification--An Experimental Study", D. V. Punwani, S. P. Nandi, L. W. Gavin and J. L. Johnson, presented at 85th National Meeting of the American Institute of Chemical Engineers, June 4-8, 1978, Philadelphia, Pennsylvania. The teachings of these papers recognize the desirability for converting peat to SNG in that the fraction of carbon converted during a short residence time gasification is about two and one-half times higher than that converted during lignite gasification and therefore, during conversion of peat to SNG less peat char will have to be gasified than in coal to SNG conversion processes. Further, these results have shown that the maximum carbon conversion to SNG can be achieved at temperatures a few hundred degrees less than required for lignite. Conversion of peat to SNG also requires less methanation than required for lignite since the fraction of carbon converted to hydrocarbon gases (methane, ethane and ethylene) is about four times greater than for lignite. It has also been found that hydrogasification of peat may be achieved at much lower pressures than required in coal gasification. The prior art has considered only maximization of gasification from peat and has not, previous to this invention, considered the overall energy utilization of peat, including the quality and method of production of hydrocarbon liquid fuels and medium Btu gases.
Nathan, U.S. Pat. No. 2,933,822 teaches treatment of carbonaceous solids such as coal, shale, lignite and oil sands in a fluidized bed for production of gas, a tar product and a char product by pretreating under oxidation conditions at 600.degree. to 825.degree. F. and carbonization at 700.degree. to 2400.degree. F. followed by cooling the hot char. Cahn et al, U.S. Pat. No. 3,993,457 teaches gasification of coal or liquid high boiling petroleum residues by contact with injected steam in a fluidized bed at 1000.degree. to 2000.degree. F. to result in crude synthesis gas which may be subjected to a water gas shift conversion. Again, the prior art has not, previous to the present invention, considered the overall energy utilization of peat, including the quality and method of production of hydrocarbon liquid fuels and medium Btu gases.
It is an object of this invention to provide a process and apparatus for increasing the overall energy utilization of peat by increasing or decreasing, as desired, production of hydrocarbon liquid fuels including gasoline and gasoline blending feed stock.
It is another object of this invention to provide a process and apparatus providing higher overall energy efficiencies than obtained with prior peat gasification processes which were only concerned with maximizing production of synthetic natural gas.